ActiveRecord Associations Question

Question

I'm new to rails and have volunteered to help out the local High School Track team with a simple database that tracks the runners performances. For the moment, I have three models: Runners, Race_Data and Races. I have the following associations.

Runners have_many Race_Data
Races have_many Race_Data

I also want create the association Runners Have_Many Races Through Race_Data, but as my look at the diagram I have drawn, there is already a many to one relationship from Race_data to Races. Does the combination of Runners having many Race_Data and Race_Data having one Race imply a Many_to_Many relationship between Runners and Races?

Answer 1

The relationship you describe is implied, but using it involves more complex code than might be needed. I think you want something more like

class Runner < ActiveRecord::Base
  has_many :entries
  has_many :races, :through => :entries
end
class Race <  ActiveRecord::Base
  has_many :entries
  has_many :runners, :through => :entries
end
class Entry < ActiveRecord::Base
# I suggest this is a more expressive name than "Race_Data"
  belongs_to :runner
  belongs_to :race
end

That should be enough to do stuff like this:

bob = Runner.new(:name=>'Bob')
joe = Runner.new(:name=>'Joe')
race = Race.new(:race_date=>'20100313')
race.entries.create(:runner=>joe, :position=>1)
race.entries.create(:runner=>bob, :position=>2)
bob.races.all #=> [#<Race id: 1, race_date: "2010-03-13"]
bob.entries.all #=> => [#<Entry id: 2, runner_id: 1, race_id: 1, position: 2]